Imitation textured products, prepared from low cost raw material, have been proposed to replace the more costly natural food products. The most prolific development has occurred within the field of imitation meat products.
The early synthetic meat-like extrudate technology involved forming a vegetable protein slurry (e.g. soy flakes and water), mechanically working the soy flour and water within the barrel of an extruder under elevated pressures and temperatures to form a molten mass and extruding the molten mass through an orifice into the atmosphere. This resulted in a puffed extrudate which simulated the fibrous character of meat products.
Subsequently issued patents modified the extrusion process to produce a non-expanded, meat-like extrudate. U.S. Pat. No. 3,886,299 by Feldbrugger et al. discloses a dense, substantially unpuffed fibrous, meat-like product. The Feldbrugger et al. process initially entails forming a dough of the water and proteinaceous material. The dough is then fed to an extruder equipped with a heated channel of decreasing volume adapted to simultaneously elongate and thermally coagulate the dough and to release the compression without forcing the dough through a die while maintaining the pressure drop below 100 psi. Although Feldbrugger et al. infer the water content may broadly range between 20% and 65%, the working examples show that from 25% to 38% water is needed to form the fibrous dough and meat-like product. In U.S. Pat. No. 3,950,564 by Puski et al. an extrusion process for producing a dense, fibrous, meat-like substitute is also disclosed. The dense, fiberous extrudate of Puski et al. is reportedly achieved by passing a protein 50-70%/water 30-50% mix through a plurality of zones decreasing pressures and temperatures. The final zone, preceding the shaping die, is reportedly maintained at a pressure of less than 100 psi and a temperature less than 212.degree. F. Puski et al. speculate that the higher moisture content, reduced temperatures, extensive shearing action, open space within the extruder barrel, step-wise pressure reduction contributes to textural improvements. Puski et al. stresses that the configuration of the annular spacing between adjacent screw sections of the final, notched, tapered screw or cone section of the extruder and alignment of the open section within the barrel preceding the extrusion die head contributes to an extrudate having a more elongated, fibrous mass, plate-like structure.
In the preparation of these meat-like extrudates, the extruder design, extrusion conditions and the composition of the feed materials are especially adapted to produce a fibrous, meat-like structure in the finished product. Considerable mechanical working and exposure of the molten mass to frictional forces contributes to the creation of the desired fibrous character. Although this extrusion technology is suitably adapted for preparing synthetic meat-like products, it is inapplicable to the preparation of imitation vegetable products.
In view of the high cost of many vegatable products such as mushrooms, the inventors desired to produce imitation vegetable products from a low-cost raw material. In pursuit of this objective, the inventors discovered that under certain carefully controlled extrusion conditions it was possible to produce an extrudate which simulated the eating, flavor and textural attributes of a high quality vegetable product.